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HelicopterGasser Model RC HelicoptersOther › DIAPHRAGM Maintenance...
03-22-2009 04:52 PM  8 years agoPost 21
TheRickster

rrApprentice

Beaumont Texas

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On every Tilly, Walbro, Bing, Zama, etc.. I have ever fooled with the low needle has a greater effect on the high needle than the high needle does on the Low.. That would indicate to me that even at higher throttle blade opening the lo needle is still active via drafting through the venturi. All this info is via my less than scientific testing..

Rick

If in doubt lean it out . We don't do this to save money, we save money to do this

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03-22-2009 07:54 PM  8 years agoPost 22
AceBird

rrElite Veteran

Utica, NY USA

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That would indicate to me that even at higher throttle blade opening the lo needle is still active via drafting through the venturi.
The low needle goes to the three bottom ports in the throat of the carb and are well below the venturi. The three bottom ports deliver fuel because the throttle plate creates an obstruction in the carb much the same way a choke does. As it opens the obstruction goes away, again just as it does on the choke butter fly. In most two cycle engines you would set the high needle WFO and you set the low needle for a good idle then you adjust the high for a good transition. At idle there is very little air going through the carb so nothing comes through the high needle port.

You can shut off the high needle and idle or you can shut off the low and run WFO but you cannot transition from one to the other without both.

Ace
What could be more fun?

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03-23-2009 03:04 AM  8 years agoPost 23
FloridaHeli

rrVeteran

jacksonville,​florida

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iskoos,

I have a WT 643 also. Thanks for the kit no. K20-WAT. I'll try to get one local tomorrow.


Tom_in_Cincy,

Wow, That's a log of great info. I'm going to see if I can get the gage and pressure test kit tomorrow. If not I'll get them off e-bay as per your note.

What would you say is wrong with a Zenoah 231 engine in a heli that has good power in vertical climb, starts easy, good idle but not perfectly smooth and the heli gets the shakes every once in awhile while flying engine speeds from 10,800 to 12,700 rpm? I want to get the shakes out of it. Oh, I've checked the screen and it is clean. I use a fuel magnet in the tank and have a 2 screen filter inline to the carb.

When you state
When tuning the carb set both needles to about a turn and a half out to start. Always set the low speed needle first. Then the high speed
what should I be looking/listening for when setting the low and high needles? smooth idle, fast idle, slowest idle?

I just know I'm close to getting this bird running great. Just need to get this intermittent shaking eliminated.

Thanks for your previous posts and any additional info you can share.

Tom

This hobby is WAY too expensive!!

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03-23-2009 03:44 AM  8 years agoPost 24
TheRickster

rrApprentice

Beaumont Texas

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The low needle goes to the three bottom ports in the throat of the carb and are well below the venturi. The three bottom ports deliver fuel because the throttle plate creates an obstruction in the carb much the same way a choke does
So you do not feel that at a higher throttle blade opening that the air velocity moving through the venturi will not form a low pressure area above the 3 lo speed fuel feeds thus makeing them active as well?

Rick

If in doubt lean it out . We don't do this to save money, we save money to do this

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03-23-2009 04:33 AM  8 years agoPost 25
Tom_in_Cincy

rrNovice

Cincinnati Ohio

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Hi FloridaHeli I saw your other post about the needles. My first thought was maybe you had some sort of resonance in the Predator. I have 2 Vario Benzin Trainers and they shake a bit too. One is in a Bell Jet Ranger and it had a bad tail vibration at certain RPM until a big carbon rod was added to stiffen it up. Are you hearing the motor change sound when it starts shaking? What do you see shaking?
It sounds like you got the engine adjusted well according to your description. I would change out the plug and set the gap @ .025" as has been recommended since the cost is low. When setting the low speed needle you may need to move the throttle baffle a few clicks either way to be sure the right amount of air is getting into the motor. For example if the throttle is closed too far at idle you can still get it to run by over leaning the low speed needle. But it will suffer on starting and transition. If the engine starts easy, idles low enough to disengage the clutch, seems (sounds) like its hitting on most every stroke, and transitions well I'd say its set. When adjusting the high needle I set it first to break into 4 cycle every once in a while. Then slowly lean it out maybe 10 degrees of turn per flight until it stops breaking in 4 cycle. When a Walbro is working properly the needles do not have a broad tuning range, instead they are quite narrow. Broad tuning range is a sure sign of carb problems.

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03-23-2009 04:00 PM  8 years agoPost 26
Luis104

rrApprentice

Caracas / Venezuela

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I was told in a Shindaiwa store about DIAPHRAGM Maintenance; To protect the diaphragm and all the carburetor it self, you must take off all the fuel froom it running the engine with the emty tank untill the carburetor runs out of fuel; before finishing the flight day. Doing this it`s suposed to extend the diaphragm life.

Anyone is agree with this??? I´ve never done this to my XL-1005 friends have told me to leve the carburetor with fuel to mantain the diaphragm wet to protect it.

remember Shindaiwa engines use the same Walbro carbuteror we use in Zenoah engines (the only difference seems to be the throttle arm)

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03-23-2009 06:43 PM  8 years agoPost 27
Luis104

rrApprentice

Caracas / Venezuela

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if anyone is interested this is the link for the walbro carburetos maintenence manuals:

http://wem.walbro.com/distributors/servicemanuals/

the page contains a list of walbro carburetors models, the one that uses the zenoah 230puh is the WA series.

at the end of the page there is a Diaphragm carburetor maintenence manual. it has a description of how the carbutetor works and a detailed step by step procedure to change the diaphragm and calibration of the carburetor

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03-23-2009 09:00 PM  8 years agoPost 28
iskoos

rrKey Veteran

Orlando, FL

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What I would like to know is what grade fuel everybody is using.
Is the regular(87 octane) consensus?

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03-23-2009 09:13 PM  8 years agoPost 29
j.8

rrVeteran

Denmark

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Hi luis104

Thanks for the walbro link, only thing I would like
to ad, is that some zenoah 231puh uses the WT type,
anyway great link

Oktane number, here in europe we have 2 oktane numbers,
RON (research oktane number) and, MON (motor oktane number)
meaning that all the gassolin have both numbers, and the closer
the 2 numbers are, the less the risk for engien knocking.

Regards Bo

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03-24-2009 12:43 AM  8 years agoPost 30
AceBird

rrElite Veteran

Utica, NY USA

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I was told in a Shindaiwa store about DIAPHRAGM Maintenance; To protect the diaphragm and all the carburetor it self, you must take off all the fuel froom it running the engine with the emty tank untill the carburetor runs out of fuel; before finishing the flight day. Doing this it`s suposed to extend the diaphragm life.
I use to do that with my planks and had years of successful runs with the same carb. It may be because the fuel today has more alcohol in it with is rough on plastics.
So you do not feel that at a higher throttle blade opening that the air velocity moving through the venturi will not form a low pressure area above the 3 lo speed fuel feeds thus makeing them active as well?
I think yes to this question. The venturi creates low pressure at the venturi not above or below it. The velocity of the air speeds up going through the venturi (where there is a restriction) and then slows down after it.

Ace
What could be more fun?

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03-24-2009 12:31 PM  8 years agoPost 31
TheRickster

rrApprentice

Beaumont Texas

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Quote
--------------------------------------------------------------------------------

So you can see the low speed jets are always supplying fuel to the engine even when the throttle is wide open.
--------------------------------------------------------------------------------

This isn’t always the case and more than likely not the case with most carbs. Although the ports are open the barometric pressure (vacuum) goes to near 0 in this region as the butterfly opens. When the butterfly is near the closed position it acts similar to a choke which supplies the vacuum to suck out the fuel from these three holes. On the other hand the high speed jet is increasing in vacuum as the butterfly opens due to the venturi effect. There is truly a transition from the low needle to the high needle and the better that is the more reliable the engine will be when you punch it and let off. It is easy to say your hover is one needle or the other but in reality it is both. Depending on a bunch of different parameters more influence may be the low on one model and the high on another but for sure it is both because you are likely in transition.

You can clearly see that the more power to weight the engine has to lift the more hover will be towards the low needle. In other threads, people are claiming that hover is around 30% open. If this is the case you are well on to the high needle if not totally off the low needle. I can’t imagine any camera ship hovering off the low needle.

Ace
Walbro seems to be sure that the lo feeds are active at WOT..

If in doubt lean it out . We don't do this to save money, we save money to do this

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03-25-2009 10:14 PM  8 years agoPost 32
AceBird

rrElite Veteran

Utica, NY USA

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Walbro seems to be sure that the lo feeds are active at WOT..
I don't think that is what Walbro says in black and white.

From their service manual:
Note: Depending on the carburetor design the idle circuit may or may not deliver fuel at wide open throttle.
Sometimes it pays to read the words rather than interpret just a picture. Walbro has no way of telling what you will add on the carb (V-Stack, filter or any other restriction which will affect the pressure in the throat of the carb and affect how much spills out the low needle ports.) However, no matter what comes out the low ports at WOT it is small in comparison. It decreases as the throttle opens While the air volume increases tremendously. The venturi on the other hand causes the fuel delivery to increase with increasing flow from the high speed jet so the mixture stays constant. If the low speed jets didn't drop off quickly and lasted for the full throttle actuation it would screw up the mixture ratio that needs to stay constant.

Ace
What could be more fun?

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03-26-2009 12:12 AM  8 years agoPost 33
TheRickster

rrApprentice

Beaumont Texas

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You are correct Walbro does say the the Idle may or May not suppply at WOT depending upon the carburetor design. That means that it might not supply at WOT if the carb is a SDC,BDC,WG,WB, etc...

BUT the illustration clearly states the Carb as a WT series which is what the 643 and 644 series are which is what we are discussing here in the gasser forum..

Either way, adjust the needles however you see fit, makes no difference to me..I will continue to adjust them like I have for many years..

Later all,
Rick

If in doubt lean it out . We don't do this to save money, we save money to do this

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03-26-2009 09:59 PM  8 years agoPost 34
AceBird

rrElite Veteran

Utica, NY USA

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BUT the illustration clearly states
I think you are making more assumptions. An illustration is an illustration it doesn’t state anything. The prefix letters of the carbs denotes a series not the detailed design of a carb. The illustration shows a choke for instance. The 643 doesn’t have a choke which is less of a restriction in the carb bore. The choke in itself, like a filter will have a tendency to draw more from the low needle ports and without a choke draw less.

For people that have dealt with these engines for a long period of time it doesn’t matter. They are successful with whatever they have been doing. For those that are new, it is a different story. They have to learn the idiosyncrasies of these two cycle engines and how they are used in helicopters. Making assumptions based on the trial and error method is not always the best route to take.

It is my belief that most engines are burned up because the high needle is set wrong and not so much the low. People are fooled into thinking that because it takes less of a change to the low needle to see a different result that it is more critical than the high. It takes less of a change to the low needle because there is so little air volume at low speeds. The fact of the matter is the low needle can be sloppy rich or even a tad lean and not do damage to the engine where as if the high needle is sloppy rich or a tad lean you are a goner. When you reach the point where the cooling system can not take the heat away fast enough it is like falling of a cliff.

Ace
What could be more fun?

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03-29-2009 08:01 PM  8 years agoPost 35
Fixit

rrElite Veteran

UK

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I was amazed last week to find the diaphragm on my 600 gasser had perished after only a gallon and a half of fuel.

The heli started to lean out and I checked the muffler, carb gaskets and fuel lines but still had the same problem, the gauze filter was clear so I pulled the pump diaphragm off and it was limp and distorted , I have another new 231 in the 700 I’m building so I swapped the diaphragm and its run fine this weekend, I cant believe this could happen after such a sort time but seeing is believing.

I only like to fly gassed up

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03-29-2009 08:16 PM  8 years agoPost 36
pgkevet

rrKey Veteran

Wales

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I was amazed last week to find the diaphragm on my 600 gasser had perished after only a gallon and a half of fuel.
Got a feeling some plastic moulding processes use a release agent? Any chance the fuel picked up something from inside the 600's default tank? Might be worth soaking a new tank and dumping the petrol into your car on the next build??

pgk

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03-29-2009 08:41 PM  8 years agoPost 37
Fixit

rrElite Veteran

UK

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Any chance the fuel picked up something from inside the 600's default tank?
I suppose that could be possible but I rather think it was an inferior diaphragm.

I should complain to Rossendale Models who supplied the engine but it will be less hassle just to order a carb kit.

I only like to fly gassed up

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03-29-2009 10:37 PM  8 years agoPost 38
JuanRodriguez

rrProfessor

The Villages,​Florida

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I pulled the pump diaphragm off and it was limp
I can't imagine the wife was pleased either !...

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03-29-2009 10:46 PM  8 years agoPost 39
bosshoss

rrVeteran

Chicago, IL

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Was the pump diaphragm the black rubber one? The edges curl up on the pump flappies.

Directly related to how much alcohol is in the fuel. IMO.

While the black one works best when new, it lasts the least. AND, you can't get the black one in the re-build kits.

Why Hover a Yak, when a Heli does it better?

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03-29-2009 10:55 PM  8 years agoPost 40
Fixit

rrElite Veteran

UK

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I can't imagine the wife was pleased either !...
Are they ever
Was the pump diaphragm the black rubber one
Yes

I only like to fly gassed up

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